1. Field of the Invention
The present invention relates to an impact crushing machine for finely and effectively pulverizing materials such as small blocks of calcium carbonate, talc, graphite and silicone.
2. Description of Prior Art Technique
Most of the high speed rotary type impact crushing machines represented by the name of a pin mill, a hammer mill and the like have a large crushing ratio (diameter of raw materials/diameter of pulverized materials), an extremely short crushing tie or staying time as compared with a grinder type crushing machine and simple handling operation, and hence, are widely used as continuous type crushing machines.
The pulverized grain grade obtained by the high speed rotary impact crushing machine is generally of the order of several 100.mu. because of the following reasons (1) to (3), and the distribution thereof is also extremely widely scattered.
(1) Since the crushing mechanism is of a so-called one-passs type having an extremely short stating time and utilizes the volume crushing using instantaneous knock, there are materials given impact and materials not given impact sufficiently. The distribution of the pulverized grain grade is widely scattered and the average diameter of the pulverized grain is large.
(2) There is a case, wherein the machine is provided with a screen (punched porous plate) to regulate the grain grade. However, the basic crushing mechanism is of the one-pass type and utilizes the volume crushing in the same manner as the above item (1), and the minimum diameter of the screen is limited to about 200.mu. because of problems of manufacturing and use thereof (blocking meshes of the screen). Accordingly, the limitation of the crushable diameter is about 100.mu..
(3) The materials are also repeatedly crushed by the impact type crushing machine (multi-crushing). Since the distribution of the crushed grain grade is widely scattered, fine grains serve as cushions for materials having large diameter to be crushed and the diameter of the materials to be crushed is reduced.
Heretofore, a classifier is also used together with the crushing machine. In general, materials tend to cohere with each other and are difficult to be separated from each other as the materials are fine grains. Accordingly, the pulverized grains are difficult to be separated from each other and the diameter of the pulverized grain is of the order of several tens micron. Further, if the classification accuracy is increased to obtain fine grains, a great number of coarse grains cut by the classification are left and stable operation can not be performed effectively.
It is thus difficult for the one-pass and high speed rotary type impact crushing machine in the prior art to obtain finely pulverized materials having a uniform diameter of the order of one micron or sub-micron.